1. Field of the Invention
This invention relates to a current control apparatus and a manufacturing method for the current control apparatus, with which a reduction in current detection precision due to the effects of heat generated by a switch element is suppressed, thereby enabling highly precise current detection such that an amount of current supplied to a connected inductive element can be controlled with a high degree of precision.
2. Description of the Related Art
An inverter or the like performs drive control on a motor by switching a current supply path along which a current is supplied from a power supply to respective coils of the motor by controlling a switch element. Further, by controlling a switch element, a transformer or the like adjusts an amount of current supplied from a power supply to a reactor, transforms a voltage generated by a power supply into a desired voltage, and outputs the desired voltage.
A motor or a transformer is formed from an inductive element (typically a coil). To control a torque of the motor, for example, an amount of current supplied to the coil is controlled.
A current control apparatus controls the amount of current supplied to the coil to a desired value by detecting the amount of current supplied to the coil as a current value and controlling a switch element on the basis of the detected current value.
The detected current value used during current control is obtained by a magneto-electric transducer attached to a core penetrated by a bus bar disposed in the current control apparatus.
When the bus bar is energized, a magnetic field corresponding to the current value is generated. The magneto-electric transducer detects the generated magnetic field via the core, and converts the magnetic field into a voltage corresponding to the magnetic field. Further, the voltage converted by the magneto-electric transducer is output to control means, whereupon the control means calculates a current flowing through the coil from the input voltage and controls the current.
Incidentally, an in-vehicle inverter is preferably capable of highly precise motor control in order to realize favorable operability and efficiency. To realize highly precise motor control, the current must be detected with a high degree of precision. The current detection precision is affected by the magnetic field detection precision of the magneto-electric transducer. The magnetic field detection precision is affected by characteristics of the magneto-electric transducer as well as the positional precision of the core and the magneto-electric transducer.
For example, a method for improving the positional precision of a core and a magneto-electric transducer by molding the core integrally with a case so that the core is fixed reliably has been proposed in the prior art (see Japanese Patent Application Publication No. 2007-028785, for example). Japanese Patent Application Publication No. 2007-028785 indicates that when the case and the core are molded integrally, the core can be prevented from moving in response to vibration generated during vehicle travel, and as a result, a distance between the core and the magneto-electric transducer can be kept constant at all times.
According to Japanese Patent Application Publication No. 2007-028785, therefore, a current can be detected with a high degree of precision without being affected by magnetic variation caused by movement of the core. As a result, current control can be performed with a high degree of precision, enabling highly efficient control motor control.